Light-emitting polymer

ABSTRACT

A radiation-emitting polymer composition includes a polysiloxane polymer including tritium and a wavelength-shifter chemically bonded as a side chain to the polysiloxane polymer or chemically bonded as a side chain to a siloxane carrier dispersed within the polysiloxane polymer. The wavelength-shifter includes a plurality of cyclic chemical moieties and emits electromagnetic radiation in response to radiation emitted by the tritium.

RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.13/391,450, filed on Oct. 2, 2011, which is a United States NationalPhase of PCT Application No. PCT/US10/46276, filed on Aug. 23, 2010,which claims priority to U.S. Provisional Application No. 61/235,729,filed on Aug. 21, 2009.

BACKGROUND OF THE INVENTION

This disclosure relates to light-emitting polymers for use as light orenergy sources.

Light-emitting polymers are known and used for self-illuminated signs,“nuclear” batteries, and the like. As an example, conventionallight-emitting polymers may be formed from polystyrene and labeled withtritium that emits radiation, such as beta particles. The polymer isdoped with a scintillator, such as a phosphor, that emits visible lightwhen irradiated with the radiation from the tritium. That is, thelight-emitting polymer is self-illuminating and may be used for signs orwith photovoltaic devices to generate electric current.

SUMMARY

A radiation-emitting polymer composition includes a polysiloxane polymerincluding tritium and a wavelength-shifter chemically bonded as a sidechain to the polysiloxane polymer or chemically bonded as a side chainto a siloxane carrier dispersed within the polysiloxane polymer. Thewavelength-shifter includes a plurality of cyclic chemical moieties andemits electromagnetic radiation in response to radiation emitted by thetritium.

Also disclosed is an energy source that includes an electromagneticradiation-emitting polymer having a polysiloxane polymer that includestritium and a wavelength-shifter chemically bonded as a side chain tothe polysiloxane polymer or chemically bonded as a side chain includes aplurality of cyclic chemical moieties and emits electromagneticradiation in response to radiation emitted by the tritium. Anelectromagnetic-responsive device is adjacent to the electromagneticradiation-emitting polymer and is operable to provide an electriccurrent in response to the electromagnetic radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example light-emitting polymer.

FIG. 2 illustrates an example energy source that includes alight-emitting polymer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates selected portions of an example light-emittingpolymer 20, which may be used as a light source or an energy source forproviding electric current, as will be described later in thisdescription. One premise of this disclosure is that the exemplarylight-emitting polymer 20 provides greater stability than previouslyknown light-emitting polymers and is more efficient in generating light.The term “light,” “illuminate” and variations thereof as used in thisdisclosure may refer to all forms of electromagnetic radiation, such asultraviolet and visible radiation, and are not limited toelectromagnetic radiation within the visible wavelength spectrum.

As indicated above, the light-emitting polymer 20 emits light 22 and isthereby self-illuminating. For instance, the light-emitting polymer 20includes polysiloxane with tritium bonded thereto that emits radiation,such as beta particles. A wavelength-shifter may be chemically bonded tothe polysiloxane polymer. The wavelength-shifter emits light, such asultraviolet or visible light, in response to the radiation emitted fromthe tritium. The polysiloxane polymer may also include other additives,depending upon the intended use of the light-emitting polymer 20, suchas cross-linking agents, plasticizers, anti-oxidants, and the like.

The polysiloxane is durable and less susceptible to cross-linking ordegradation from the emitted radiation than prior light-emittingpolymers. For instance, former light-emitting polymers based onpolystyrene exhibit limited durability because the radiation causescross-linking and “color centers” that reduce light emission. Incomparison, the radiation does not cause significant cross-linking or“color centers” in polysiloxane and the disclosed light-emitting polymer20 may thereby exhibit little reduction in functionality over a periodof at least several years.

In the illustrated example, the wavelength-shifter is chemically bondedto the polysiloxane polymer. In other words, the wavelength-shifter isnot merely doped into or mixed with the polymer but is insteadchemically bonded to the polymer monomer. The wavelength-shifter haslimited solubility within the polysiloxane polymer if physically mixedwith the polymer or doped into the polymer. Thus, chemically bonding thewavelength-shifter to the polysiloxane polymer avoids the solubilitylimitation and thereby allows a greater amount of the wavelength shifterto be incorporated into the light-emitting polymer 20. Thelight-emitting polymer 20 is thereby capable of more efficientlyconverting the radiation emitted from the tritium into light.

In one example, chemically bonding the wavelength-shifter to thepolysiloxane polymer permits a concentration of wavelength-shifter ofapproximately 0.015 gram/gram in the polysiloxane. In one specificexample, the concentration of wavelength-shifter may be about 0.75 gramsin about 50 grams of polysiloxane.

The tritium may alternatively be incorporated into the light-emittingpolymer 20 through use of a tritium carrier. The tritium carrier may bethe reaction product of divinyltetraphenyldisiloxane with tritium. Anexample of this reaction is shown below in equation 1.

H₂C═CHSi(C₆H₅)₂OSi(C₆H₅)₂CH═CH₂+³H₂+³H₂→³HH₂CCH³HSi(C₆H₅)₂OSi(C₆H₅)₂CH³HCH₂³H   Equation (1)

The tritium carrier may then be mixed with a siloxane monomer, which isthen polymerized in a known manner to form the light-emitting polymer20. The tritium carrier is not chemically bonded to the polysiloxanepolymer but is compatible with the polymer through the use of the samechemical side groups on the siloxane monomer and on the carrier. In thiscase, each of the siloxane monomer and the carrier may include phenylgroups and siloxane groups for compatibility. Thus, the carrier may bindto the polysiloxane through secondary bonding that involves attractionbetween the chemical side groups.

The wavelength-shifter may be any type of wavelength-shifter that issuitable for chemically bonding with the polysiloxane polymer, orsiloxane monomer during a preparation stage of the light-emittingpolymer 20. As an example, the wavelength-shifter may be1-phenyl-3-mesityl-2-pyrazoline, or PMP. An example structure of a PMPmolecule is shown below as wavelength-shifter 1.

In one modification, the PMP molecule may include additional side groupsthat may facilitate compatibility with the polysiloxane polymer orreaction with the siloxane monomer to attach the wavelength-shifter tothe monomer. As an example, the structure of an example modified PMP isshown below as wavelength-shifter 2.

In one example of the preparation of the light-emitting polymer 20, asiloxane monomer and the desired additives may be mixed with the tritiumcarrier and the selected wavelength-shifter to bond thewavelength-shifter to the siloxane monomer. The wavelength-shifterreacts with the siloxane monomer to replace one of the phenyl groups orattach to one of the phenyl groups in a chemical bond. The mixture maybe heated to facilitate the reaction and known laboratory ormanufacturing equipment may be utilized to carry out the preparation. Anexample of the preparation of a wavelength-shifter 1 bonded to thepolysiloxane is shown below, where m and n are each integers greaterthan or equal to one.

The siloxane monomer may also be selected for compatibility with thewavelength-shifter. As an example, the siloxane monomer may include oneor more side groups that function as reaction sites for chemicallyreacting with the wavelength-shifter to bond the wavelength-shifter tothe polysiloxane backbone. The siloxane monomer structure illustratedbelow, a phenylsiloxane, may be used in combination with the abovewavelength-shifters to form the light-emitting polymer 20 as tritiatedpolyphenylsiloxane.

Alternatively, or in addition to bonding the wavelength-shifter to thepolysiloxane backbone, the wavelength-shifter may be chemically bondedto a siloxane carrier that is then dispersed within the polysiloxanepolymer. In one example of the preparation of the light-emitting polymer20, a siloxane monomer and the bonded wavelength-shifter/siloxanecarrier are mixed together with the tritium carrier to disperse thebonded wavelength-shifter/siloxane carrier uniformly throughout thepolysiloxane polymer. The mixture may be heated to facilitate theprocess and known laboratory or manufacturing equipment may be utilizedto carry out the preparation.

As an example, the bonded wavelength shifter/siloxane carrier form thechemical structure shown below (where WS is the wavelength-shifter):

In another example where the wavelength-shifter is chemically bonded tothe siloxane carrier, the wave-length shifter/siloxane carrier form thechemical structure below (where WS is the wavelength-shifter):

FIG. 2 illustrates one example implementation of the light-emittingpolymer 20 in an energy source 30 for generating electric current. Inthis example, the light-emitting polymer 20 is located adjacent to aphotoelectric device 32, such as a photovoltaic cell or photocell. Thelight 22 emitted from the light-emitting polymer 20 impinges upon alight-receiving surface 34 of the photoelectric device 32, whichconverts the light into electrical energy. In this case, thephotoelectric device 32 is shown in a spaced arrangement relative to thelight-emitting polymer 20 and only on one side of the light-emittingpolymer 20. However, in other examples, the photoelectric device 32 maybe in intimate contact with the light-emitting polymer 20 or designed tosurround the light-emitting polymer 20 such that the photoelectricdevice 32 receives light emitted from all sides of the light-emittingpolymer 20. Thus, the illustrated arrangement may be adapted to suit theparticular needs of an intended application.

Additionally, the photoelectric device 32 may be any type ofphotoelectric device or array for receiving the light 22 and convertingthe light 22 into electrical energy. For instance, the photoelectricdevice 32 may include specialized photocells that are adapted forabsorbing light within a specific wavelength range to efficientlyconvert the light 22 into electrical energy.

In some examples, the light-emitting polymer 20 may exclude ascintillant or wavelength-shifter and rely on the chemical side groupsof the polysiloxane polymer, such as the phenyl groups, to convert theradiation emitted from the tritium into light. In this case, the light22 emitted may be in the ultraviolet wavelength range and thephotoelectric device 32 may therefore be adapted to convert ultravioletradiation into electrical energy. In this regard, the photoelectricdevice 32 may include quantum dot photocells for absorbing light 22within the ultraviolet wavelength range.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure.

What is claimed is:
 1. A radiation-emitting polymer compositioncomprising: a polysiloxane polymer including tritium; and awavelength-shifter chemically bonded as a side chain to the polysiloxanepolymer or chemically bonded as a side chain to a siloxane carrierdispersed within the polysiloxane polymer, the wavelength-shifterincluding a plurality of cyclic chemical moieties and emittingelectromagnetic radiation in response to radiation emitted by thetritium.
 2. The light-emitting polymer composition as recited in claim1, wherein a concentration of the wavelength-shifter in the polysiloxanepolymer is approximately 0.015 gram/gram.
 3. The light-emitting polymercomposition as recited in claim 1, further comprising a tritium carrierbonded with the tritium, and the tritium carrier isdivinyltetraphenyldisiloxane.
 4. The light-emitting polymer compositionas recited in claim 1, wherein the wavelength-shifter is chemicallybonded to the siloxane carrier, and the siloxane polymer and thesiloxane carrier each comprise phenyl groups.
 5. The light-emittingpolymer composition as recited in claim 1, wherein thewavelength-shifter comprises 1-phenyl-3-mesityl-2-pyrazoline.
 6. Thelight-emitting polymer composition as recited in claim 1, wherein thewavelength-shifter comprises:


7. The light-emitting polymer composition as recited in claim 1, whereinthe wavelength-shifter is chemically bonded to the polysiloxane polymerto form:

wherein m and n are each integers greater than or equal to
 1. 8. Thelight-emitting polymer composition as recited in claim 1, wherein thepolysiloxane polymer is a polyphenylsiloxane.
 9. The light-emittingpolymer composition as recited in claim 1, wherein thewavelength-shifter is chemically bonded to the siloxane carrier to form:

wherein WS is the wavelength-shifter.
 10. The light-emitting polymercomposition as recited in claim 1, wherein the wavelength-shifter ischemically bonded to the siloxane carrier to form:

wherein WS is the wavelength-shifter.
 11. An energy source comprising:an electromagnetic radiation-emitting polymer comprising a polysiloxanepolymer including tritium and a wavelength-shifter chemically bonded asa side chain to the polysiloxane polymer or chemically bonded as a sidechain to a siloxane carrier dispersed within the polysiloxane polymer,the wavelength-shifter including a plurality of cyclic chemical moietiesand emitting electromagnetic radiation in response to radiation emittedby the tritium; and an electromagnetic-responsive device adjacent to theelectromagnetic radiation-emitting polymer and operable to provide anelectric current in response to the electromagnetic radiation.
 12. Theenergy source as recited in claim 11, wherein theelectromagnetic-responsive device comprises quantum dot photocells forabsorbing light within an ultraviolet wavelength range.